A variety of compositions and processes have been developed to form steels that can meet the demanding performance characteristics required for aircraft landing gear. Steels that are used for landing gear are generally martensitic steels, and the steels used for landing gear for commercial aircraft and for U.S. Air Force planes are low alloy steels such as 4340 and 300M. The compositions of these steels are given in Table I, below. These steels are tempered in the range of 200° C. to 300° C. and are strengthened by carbon in solid solution and the precipitation of iron carbides. They have the desired strength for landing gear but they have fairly low toughness, no corrosion resistance and low resistance to stress corrosion cracking.
About 15 years ago, the U.S. Navy started to use a new steel called AerMet 100 for the landing gear of its planes. This steel's composition is also given in Table I, below. AerMet 100 has very high strength and excellent fracture toughness and better resistance to stress corrosion cracking than 300M or 4340. However, this steel is quite expensive as it contains 13.4 wt. % cobalt and about 11 wt. % nickel.
TABLE ISteel Compositions in wt. %AlloyCCrMoWVNiSiCoMn43400.380.90.25——1.80.3—0.7300M0.380.90.3—0.081.80.3—0.5AerMet 1000.233.11.2——11.1—13.4—Ferrium M540.301.02.01.30.1010.0— 7.0—H-110.405.01.3—0.5 —1.0—0.5